Abstract: Empirical evidence from single-unit recording and functional neuroimaging points to the identity of cortical substrates for working memory (WM) and for long-term memory (LTM). Thus, that evidence informs and conforms to the neural definition of WM as the temporary activation of an updated cortical network of LTM for the pursuit of a behavioral, linguistic or logical goal. Structurally, the network is made of associations between dispersed neuronal assemblies representing the perceptual and executive components of a LTM gestalt (cognit) of goal-directed action. Functionally, the network must be orderly activated for the orderly attainment of each intermediate sub-goal. Whenever that pursuit requires the mediation of cross-temporal contingencies between percepts and acts, WM comes into play. WM consists of the persistent and recurrent activation of the network for as long as necessary to mediate those contingencies. The executive, controlling, role of the prefrontal cortex derives exclusively from its role in the representation, and therefore enactment, of complex goal-directed performance--including cross-temporal contingencies. Two forms of reentry are essential to that performance: (1) The recurrent reentry--in WM--between prefrontal (executive) and posterior (perceptual) cortical networks at the top of the perception-action cycle; and (2) The external reentry that closes that cycle at the bottom, through the environment, between motor effectors and sensory receptors.